Channel Flow Simulation using CONVERGE CFD

AIM:

To simulate the flow of air through a channel using converge CFD.

OBJECTIVE:

• To setup and run the simulation for three different grid sizes and compare the results.
• To plot velocity contour, pressure contour, mass flow rate and total cell count for all the 3 base mesh sizes.

INTRODUCTION:

CHANNEL FLOW:

Flows in conduits or channels are of interest in science, engineering, and everyday life.

There are two type of flow through conduits.

• Open channel flow
• Closed channel flow.

CLOSED CHANNEL FLOW:

Flows in closed conduits or channels, like pipes or air ducts, are entirely in contact with rigid boundaries. Most closed conduits in engineering applications are either circular or rectangular in cross section.

OPEN CHANNEL FLOW:

Open-channel flows, on the other hand, are those whose boundaries are not entirely a solid and rigid material; the other part of the boundary of such flows may be another fluid, or nothing at all. Important open-channel flows are rivers, tidal currents, irrigation canals, or sheets of water running across the ground surface after a rain.

LAMINAR FLOW:

laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface.

CASE SETUP:

• Geometry is created using geometry editing tool box under create tab.

The dimensions are filled and the geometry is created.

• The boundary are created for the geometry under boundary flag tab.

The boundaries are assigned to the faces and the name of the boundaries are edited and click apply.

• The orientation of normal are checked and its changes such that the normal points inwards by going to transform > normal

• The diagnosis is runed and checked for problems for the geometry.

• Begin case setup:
• Application type

On the right panel go to the case setup tab, select begin case setup.

Select the application type as time-based and select apply and done.

• Physical models

Select physical models and disable turbulence modelling then press apply and done.

• Materials

Select materials and unselect the checkbox reaction mechanism as we are not simulating any reactions then select the predefined mixture as air then click apply and done.

• Species

In species add O2 and N2 and press ok.

• Global transport properties

Select global transport properties, keep the default values and press ok.

• Run parameters

Under solver tab select solver as steady-state solver

Under misc. tab enable steady-state monitor and disable the used shared memory.

• Simulation time parameters

Set the start time, end time, initial, minimum and maximum time steps as shown above.

• Solver parameters

Select the navier-stokes solver type as density based and click ok.

• Regions and initializations

The regions are created and air is added as species and mass fractions are changed to O2 as 0.77 and N2 as 0.23.

• Boundary conditions

Inlet:

For inlet, set the pressure boundary condition as specified value of 100001 pa and select air for species boundary conditions.

Outlet:

Set the outlet pressure boundary conditions as specified value of 100000 pa and for species backflow select air.

Top and bottom:

Select the top and bottom boundary as wall type with no slip boundary conditions. And the temperature as specified values of 300k.

Front and back:

The boundary type is selected as 2d.

• Steady state monitor

The monitor variables are added and the minimum number of cycles, monitor start delay and sample sizes are defined.

• Base grid

The three different base grids are defined for three different cases and press ok.

• Post variable selection

Keep the default values in typical variables tab.

In species mark mass fraction and add O2 and N2 are added.

• Output files

The interval for writing 3d output data files and restarting outputs are defined.

• Exporting the input files to a folder
• Then the executable is pasted inside the folder
• The simulation is run in Cygwin for three different base mesh grid sizes.
• The postconvert executable is pasted in the output folder.
• The post conversion is done on Cygwin and converted into the type that paraview reads.
• The results are then post processed using paraview.

RESULTS:

CASE 1:

MESH:

VELOCITY CONTOUR:

From the above plot we can say that velocity is high at the centre and keeps on decreasing and lower near the walls.

PRESSURE CONTOUR:

From the above plot, the pressure is higher at inlet and lower at outlet. Due to this pressure difference the flow takes place in the channel.

VELOCITY PROFILE:

X = 0:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at inlet is 0.823m/s.

X = 0.05:

From this plot, we can say that velocity is less near the walls and higher at the centre. The flow is developing. The maximum velocity at x = 0.05m is 1.05m/s.

X = 0.1:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at outlet is 1.08m/s. The flow is fully developed and parabolic.

PRESSURE PROFILE:

From this plot, we infer that pressure decreases from inlet to outlet.

CELL COUNT:

Number of cell count is 25000.

MASS FLOW RATE:

AT INLET:

AT OUTLET:

Mass flow rate at inlet and outlet are equal and the value is 0.01kg/s. At inlet mass flow rate is negative because it flows from inlet boundary.

CASE 2:

MESH:

VELOCITY CONTOUR:

From the above plot we can say that velocity is high at the centre and keeps on decreasing and lower near the walls.

PRESSURE CONTOUR:

From the above plot, the pressure is higher at inlet and lower at outlet. Due to this pressure difference the flow takes place in the channel.

VELOCITY PROFILE:

X = 0:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at inlet is 0.43m/s.

X = 0.05:

From this plot, we can say that velocity is less near the walls and higher at the centre. The flow is developing. The maximum velocity at x = 0.05m is 0.51m/s.

X = 0.1:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at outlet is 0.5!m/s. The flow is fully developed and parabolic.

PRESSURE PROFILE:

From this plot, we infer that pressure decreases from inlet to outlet.

CELL COUNT:

Number of cell count is 45420.

MASS FLOW RATE:

AT INLET:

AT OUTLET:

Mass flow rate at inlet and outlet are equal and the value is 0.005kg/s. At inlet mass flow rate is negative because it flows from inlet boundary. Mass flow rate converges after some number of cycles.

CASE 3:

MESH:

VELOCITY CONTOUR:

From the above plot we can say that velocity is high at the centre and keeps on decreasing and lower near the walls.

PRESSURE CONTOUR:

From the above plot, the pressure is higher at inlet and lower at outlet. Due to this pressure difference the flow takes place in the channel

VELOCITY PROFILE:

X = 0:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at inlet is 0.582m/s.

X = 0.05:

From this plot, we can say that velocity is less near the walls and higher at the centre. The flow is developing. The maximum velocity at x = 0.05m is 0.69m/s.

X = 0.1:

From this plot, we can say that velocity is less near the walls and higher at the centre. The maximum velocity at outlet is 0.69m/s. The flow is fully developed and parabolic.

PRESSURE PROFILE:

From this plot, we infer that pressure decreases from inlet to outlet.

CELL COUNT:

Number of cell count is 70056.

MASS FLOW RATE:

AT INLET:

AT OUTLET:

Mass flow rate at inlet and outlet are equal and the value is 0.008kg/s. At inlet mass flow rate is negative because it flows from inlet boundary. Mass flow rate converges after some number of cycles.

ANIMATION OF VELOCITY CONTOUR PLOT:

https://drive.google.com/file/d/11UsYgjjbVQE4p5_3wNXulCnPSoWwTON0/view?usp=sharing

The animation shows how the velocity changes with respect to time.

CONCLUSION:

From all the plots we can say that as the mesh size decreases the results are becoming more accurate and it also increases the computational time.